The present invention relates to a torque wrench for additional tightening inspection.
Among inspection methods for inspecting a tightened bolt (screw) for a torque value, there is an additional tightening torque method in which the bolt in the tightened state is further tightened with a torque wrench and the torque value at which the bolt starts rotating again is read from the above-mentioned torque wrench. Incidentally, the bolt is left as it is after the inspection.
This additional tightening torque method uses such torque wrenches as a scaled torque wrench. Upon the restart of rotation, the torque value is read from the scale to check the tightening torque value of the bolt.
In this additional tightening torque method of checking the tightening torque value of a tightening bolt by using a scaled torque wrench, as shown in FIG. 5, a force in the tightening direction is applied to the torque wrench, and the bolt to be inspected (hereinafter, referred to as inspection bolt) undergoes a torque. The torque increases as shown by the broken line E.
On the other hand, in order for the inspection bolt in a stationary state to be rotated again, a torque must be applied beyond the one resulting from the static frictional resistance of the inspection bolt. Accordingly, when the tightening torque increases as shown by the broken line E to exceed the point A and the integral rotation of the torque wrench and the inspection bolt is sensed and confirmed at an additional tightening point B, the additional tightening torque measurement T2 corresponding to that point is read from the scale on the torque wrench. Based on this additional tightening torque measurement T2, the torque value (T1) at the point A is calculated, for example, by using a predetermined factor. Then, it is determined if this torque value T1 calculated equals to a desired torque value (T0) specified.
In such a conventional additional tightening torque method, the additional tightening torque measurement T2 has a difference in value with respect to the actual tightening torque value T1. Besides, the torque measurement in additional tightening at the foregoing additional tightening point B may vary. For example, when the bearing surfaces of the tightening bolt and the member to be tightened by the tightening bolt are in close contact, the additional tightening point B rises in torque indicating position on the characteristic chart of FIG. 5. This causes an increase in the additional tightening torque measurement T2.
When lubricating oil, a washer, or the like is interposed between the bearing surfaces of the member to be tightened and the tightening bolt so that the member to be tightened and the tightening bolt are in loose contact, the additional tightening point B falls in torque indicating position. The additional tightening torque measurement T2 then approaches the tightening torque value T1.
In addition, the torque indicating position of the additional tightening point B also fluctuates up and down due to variations in the rotational speed of the torque wrench depending on persons to be measured, the degrees of thermal expansion of the member to be tightened and the tightening bolt depending on air temperature, and so on. These factors also cause variations in the torque measurement T2 in additional tightening.
For this reason, the present applicant has already proposed the invention described in Japanese Patent Laid-Open Publication No. 2000-778 as a method of measuring a tightening torque which resolves such variations in the measurement T2.
This method of measuring a tightening torque is based on the assumption that in FIG. 5, when tightening is started and a stable rotating state is reached beyond the point A where the inspection bolt starts rotating again, the rotation angle and the torque value of the inspection bolt (torque wrench, in fact) trace a linear characteristic line and this characteristic line crosses the point A. At and after the point C where the rotating state is stable, the torque value corresponding to a rotation angle of the torque wrench is measured on a plurality of points. The measurement start position (xcex80) of the rotation angle is set at the point A so that the torque value at the point A can be obtained by calculation.
The torque wrench for additional tightening inspection described above, capable of measuring the rotation angle of the torque wrench to inspect the tightening torque, is based on the theory assuming that the rotation angle of the torque wrench is 0xc2x0 until the point A shown in FIG. 5 is exceeded.
Nevertheless, it is impossible for the entire torque wrench including the torque wrench body and the socket to be made into a perfect rigid body. For example, when a force is applied to the torque wrench, the torque wrench itself bends because of distortion. It follows that a certain angle of rotation is detected before the point A shown in FIG. 5 is reached.
Moreover, torque wrenches to be used for measuring a tightening torque by applying an additional tightening torque to a tightening bolt already tightened as described above vary greatly in type and characteristic.
For example, in a torque wrench such as a torque wrench for additional tightening inspection shown in FIG. 1, as an embodiment of the invention, a wrench body 2 is provided with torque detecting means and a processor 1 including a display unit for displaying the torque value detected, and is selectively combined with ratchet type replaceable heads 3, spanner type replaceable heads 4, various kinds of sockets of different lengths (not shown), or the like to measure a tightening screw for a screw tightening torque. Here, variations in the torsion angles and play angles inherent to the above-mentioned attachments to be selected in use, or the various kinds of replaceable heads and sockets, cause differences in the torsion angle characteristics and play angle characteristics of the respective measuring wrenches in use.
For example, the maker side of the torque wrench ships to the user side a predetermined wrench body 2 and attachments specified by a predetermined torsion characteristic or the like in combination as intended for the measurement of the tightening torque of a tightening screw. When the user measures the tightening torque of a tightening screw, any change will not occur in the characteristic of the wrench and the tightening torque value can be easily detected (measured) on the basis of the torsion characteristic of the torque wrench specified at the time of the shipment so long as the attachments are combined and used with the wrench body 2 as they are shipped from the maker. Depending on the working environment and the like for the tightening torque measurement, however, attachments other than those shipped might have to be substituted and used with the wrench body in measurement from sheer necessity.
In such cases, a difference can occur between the torsion characteristic etc. of the attachments substituted and used by the measurer to measure the tightening screw torque value and the torsion characteristic of the attachments mounted on the wrench body upon the shipment from the maker. Then, as shown in FIG. 6, for example, the torque wrench may start rotating at the rotation start point xcex80 before the inspection bolt actually starts rotation, thereby causing a difference in angle from the rotation start position xcex81 where the inspection bolt actually rotates again (starts additional tightening).
Consequently, an error Ts appeared in the torque value calculated corresponding to this difference in angle, and it was impossible to obtain a tightening torque value with high precision.
An object of the invention according to the present application is to provide a torque wrench for additional tightening inspection which corrects an error resulting from the rotation of a torque wrench before the rotation of an inspection bolt so that a tightening torque of the bolt can be obtained with precision by simply tightening the tightening bolt additionally.
A first invention is a torque wrench for additional tightening inspection for tightening a bolt in a tightened state, comprising: torque detecting means for detecting a torque in tightening the bolt, the torque detecting means being arranged in a wrench body; rotation angle detecting means for detecting a rotation angle of the torque wrench, the rotation angle detecting means being arranged in the wrench body; first arithmetic means for assuming a torque gradient line in a rotating state of the bolt based on input information acquired in a stable domain after the rotation of the bolt and a referential torsion characteristic gradient line set in advance, with torque information detected by the torque detecting means and the rotation angle detected by the rotation angle detecting means as the input information; second arithmetic means for assuming a torque gradient line in a stationary state of the bolt obtained from the input information before the rotation of the bolt; and third arithmetic means for determining an intersection between the torque gradient line in the rotating state obtained by the first arithmetic means and the torque gradient line in the stationary state obtained by the second arithmetic means, and determining a torque value at the intersection as a torque measurement.
A second invention is a torque wrench for additional tightening inspection for tightening a bolt in a tightened state, comprising: torque detecting means for detecting a torque in tightening the bolt, the torque detecting means being arranged in a wrench body; rotation angle detecting means for detecting a rotation angle of the torque wrench, the rotation angle detecting means being arranged in the wrench body; first arithmetic means for assuming a torque gradient line in a rotating state of the bolt based on input information acquired in a stable domain after the rotation of the bolt and a referential torsion characteristic gradient line set in advance, with torque information detected by the torque detecting means and the rotation angle detected by the rotation angle detecting means as the input information; second arithmetic means for assuming a torque gradient line in a stationary state of the bolt obtained from the input information before the rotation of the bolt; and third arithmetic means for determining, as a torque measurement, a torque value at an intersection between the torque gradient line in the rotating state of the bolt obtained by the first arithmetic means and the referential torsion characteristic gradient line when a number of pieces of the input information for arithmetic in the second arithmetic means falls below a number set in advance.
A third invention is either one of the foregoing inventions, characterized by comprising display means for displaying the torque measurement determined by the third arithmetic means.
A fourth invention is the foregoing first or second invention, characterized by comprising informing means for informing of the completion of measurement when a rotation beyond an angle set in advance is made after the rotation of the bolt.
A fifth invention is any one of the foregoing inventions, characterized in that the first arithmetic means uses the input information acquired in a domain beyond a predetermined rotation angle after the rotation of the bolt as the input information obtained in the stable domain.
A sixth invention is any one of the foregoing inventions, characterized in that the first arithmetic means determines an intersection between a torque gradient line obtained from the input information acquired in the stable domain after the rotation of the bolt and the referential torsion characteristic gradient line set in advance, and further assumes a torque gradient line in the rotating state of the bolt with a torque value obtained by multiplying a torque value at the intersection by a predetermined factor as an intersection.